1. Field of Invention.
This invention relates to a method and system for treating non-hazardous liquid waste, such as grease trap waste or raw grease grit and septage. Specifically, the invention describes a system applicable to concentrated liquid waste, such as grease trap wastewater, for removing from the water volatiles, grease, trash, solids, etc., for pre-treatment into a sewage treatment system or full treatment for direct discharge into the environment. Non-hazardous liquid waste is referred in the industry alternatively and comprises raw sewage, grease trap waste, grit trap waste, and processing waste.
2. Related Art
Food preparation, meat and food processing inherently have the byproduct of fats and grease waste. Food, grease and oils are inherent in water from processes and wash-down operations. This waste water forms an emulsion that must first pass through a grease trap, as known in the art of waste water treatment, before the outfall water is allowed to discharge into a sewer collection system. In certain smaller establishments, all sanitary sewage may likewise directed through the grease trap.
The grease trap comprises an infall pipe, which discharges the water/grease/food wastewater drainage into an underground tank capable of holding 300 to 30,000 gallons. Within the tank are barriers that trap and partially separate heavy solids (rock, grit, inorganic material such as eating utensils, personal items, etc.), floating trash (light plastics such as straws), and much of the fats, oils and grease (FOG, comprising vegetable oils, animal fat, tallow) from the food preparation/processing area drains. Periodically the grease trap becomes saturated with solids, trash and FOG's, no longer effectively trapping them, and must be drained (typically every 60-180 days) per local health regulations. A vacuum truck then drops a hose into the tank and sucks out the contents of the tank, including the floating trash, FOG/water emulsion and heavy solids. This raw liquid waste that is sucked up by the vacuum truck must then be disposed. It is this disposal to which this invention is directed, through the inventive treatment method of the raw liquid waste.
Dismissing illegal methods of disposal (dumping on open land or into a storm sewer system), there are several methods in the prior art that treat and dispose the raw waste. The oldest and simplest method is to dump the waste into an open pit, where it is mixed with ash and dirt to hydrate the mixture to form a substantially dry material, which is removed with a backhoe and placed in a landfill. This system creates a severe odor problem and takes large amounts of space in landfill areas.
Another prior art method of raw waste disposal is to dump the waste into an open pit, where it is allowed to separate by gravity. The lighter FOG is skimmed off the top, purified by a method known in the art, and recycled. The remaining concentrated wastewater is sucked out and discharged into a wastewater sewer system. The remaining bottom sludge is stabilized with flyash, removed and buried or taken to a landfill. This method likewise creates a severe odor problem, requires extensive landfill use and does not clean the water to a desired level adequate for pre-treatment requirements.
A third prior art method uses biological augmentation. In this method, microbes and surfactants are mixed with the raw waste. The surfactants break up the fat globules, allowing the microbes to surround and/or ingest the smaller pieces. Bran is often added to the mixture to provide a surface for the microbes to germinate. This process creates additional waste from the bran. Further, it has the limitation of inefficiency due to the microbes dying or becoming dormant before processing the fats, thus releasing the fats back into the wastewater causing potential blockage of the piping in the collection system. The process is expensive due to the cost of microbe replacement and maintenance (such as unclogging lines), and is difficult to regulate.
It would therefore be useful improvement of the prior art for a wastewater treatment system to remove FOG's and other solids from water from a grease trap that does not have the limitations of the prior art, including those described above.